Probably these are already on your to-do list or someone has already suggested them but still, just in case:
1) When many tabs are open and the titles are truncated, hovering over any tab should display its full title in a tooltip (as in Firefox for example).
2) "Close all tabs" and "Close all except current tab" options would be nice (again, see Firefox).
3) Taskbar thumbnail previews in Windows 7 and later should display all open tabs instead of just the focused one (similar to Firefox again).
4) How small do the tabs get when many are open? Seems to me there's no option of the tabs overflowing and the user being able to horizontally scroll through them (using arrow buttons or the mouse wheel), as in Firefox.
5) Again as in Firefox when many tabs are open it would be nice to see a drop-down menu listing all of them, allowing the user to select any one and jump to it.
6) Some sort of visual indication that a tab is being dragged would be appreciated.